CN101902415A - Method of estimation and device in the time of the frequency shift (FS) of MU-MIMO OFDMA and channel response - Google Patents

Abstract

Method of estimation and device when the present invention relates to the frequency shift (FS) of MU-MIMO OFDMA and channel response.Method of estimation and device when the frequency shift (FS) of communication system and channel response are provided, described communication system for example is the MU-MIMO communication system.A kind of alternative manner that is used to a plurality of frequency resource estimated frequency skews and channel response is provided.For one group of user of given in a shared frequencies resource frequency resource estimates channel response.In addition, be the user's estimated frequency skew in this group, wherein the channel response of the user in this group and frequency shift (FS) do not remain on the numerical value of its recent renewal.Initially, user's channel response can be that ideal channel response and frequency shift (FS) can be about zero.

Description

Method of estimation and device in the time of the frequency shift (FS) of MU-MIMO OFDMA and channel response

Technical field

The present invention relates to frequency shift (FS) and channel response and estimate, and more specifically, relate to multi-user's multiple-input and multiple-output (MU-MIMO) communication environment, for example the Long Term Evolution communication system with general carrier allocation scheme (CAS).

Background technology

It is the pith of multiple access broadband access technology that OFDM inserts (OFDMA) technology.Long Term Evolution (the 4th third-generation mobile communication standard), on up link, adopt single-carrier frequency division multiple access to insert (SC-FDMA), it is a kind of new single carrier multiple access technique that has with OFDMA system similar performance and substantially the same general structure, but it has better peak value-amplitude power ratio.When in conjunction with the MU-MIMO technology, SC-FDMA can provide very high data rate under the complexity with extraordinary spectrum efficiency and appropriateness.

Though the OFDMA facilitation channel estimating and equalization task, the strict demand of time and Frequency Synchronization becomes important problem.Time synchronized can be highly simplified in insertion by Cyclic Prefix (CP).Frequency shift (FS) between transmitter and the receiver has destroyed the orthogonality between the subcarrier, therefore produced the inter-carrier interference (ICI) that can reduce its performance consumingly, and ICI does not have direct solution.

Proposed and advised that multiple technologies are used to estimate and correct the frequency shift (FS) of up link.For example, Michele Morelli etc., " Synchronization Techniques for Orthogonal FrequencyDivision Multiple Access (OFDMA): A Tutorial Review ", Proc.ofIEEE, Vol.95, No.7 (in July, 2007) has described the iterative algorithm based on time domain space-alternating broad sense expectation maximization (TD-SAGE).Though effectively, not utilize the frequency separation of different user or most channel estimation methods be the advantage of the fact that realizes on frequency domain to disclosed time domain approach.

Exist two aspects make uplink frequency skew estimate and the correction task complicated significantly.The first, carrier allocation scheme (CAS) plays an important role in the maximum channel capacity, because based on freely distribute between the different user flexibility of available subcarrier of the different channels condition that influences each user, provides the form of " multi-user diversity ".Universal CAS allows near unrestriced allocation of carriers process, and but this process provides maximum diversity gain also makes Frequency offset estimation complicated.In addition, in up link, the mobile subscriber of each access base station will be subjected to the influence of the frequency shift (FS) of varying number.

Method of estimation and need for equipment when therefore, having the frequency shift (FS) be used for the MU-MIMO ofdma communication system and channel response.

Summary of the invention

Briefly, method of estimation and device when the frequency shift (FS) of communication system and channel response are provided, this communication system for example is the MU-MIMO communication system.An aspect according to invention provides to be used to estimate the frequency shift (FS) of a plurality of frequency resources and the alternative manner of channel response.For one group of user of given in a shared frequencies resource frequency resource estimates channel response.In addition, be the user's estimated frequency skew in this group, wherein, the channel response of the user in this group and frequency shift (FS) are not maintained at the numerical value of its recent renewal.Initially, user's channel response can be that ideal channel response and frequency shift (FS) can be about zero.

Alternatively, when satisfying predetermined threshold or when reaching the pre-determined number of iteration, stop iteration.Alternatively, be that first antenna is determined frequency shift (FS), and determined frequency shift (FS) be used at least one extra antenna then.Alternatively, carry out the step of estimating channel response and estimated frequency skew simultaneously.In an exemplary embodiment, disclosed method adopts space-alternating broad sense expectation maximization (SAGE) algorithm in frequency domain.

By the following the detailed description and the accompanying drawings of reference, with the more complete understanding that obtains for the present invention and further aspect of the present invention and advantage.

Description of drawings

Fig. 1 has described the exemplary communication environment that the present invention can operate therein;

Fig. 2 has described exemplary general carrier allocation scheme;

Fig. 3 is the flow chart of the exemplary realization of frequency shift (FS) that describe to introduce feature of the present invention and channel response estimation procedure;

Fig. 4 has described the FFT of frequency error index, f (r, ε _{M, f}); And

Fig. 5 has described the signal to noise ratio (snr) restriction of being forced by this effect, and this is restricted to the function of the number of offsetting item.

Embodiment

The present invention is by space-alternating broad sense expectation maximization (SAGE) algorithm in frequency domain, when being provided, the frequency shift (FS) that is used for exemplary MU-MIMO OFDMA up link and channel response estimate, wherein, this up link has general carrier allocation scheme.The present invention admits the cognition of frequency shift (FS) correction Technology Need channel response, and vice versa.The effective ways of having estimated when therefore, providing frequency shift (FS) and channel response.Use is obtained channel and Frequency Estimation by the training piece that each user periodically sends in uplink frame.

Further discuss in conjunction with Fig. 3, exemplary algorithm is made up of iteration and circulation.Iteration comprises a plurality of circulations.In each circulation, estimate (and renewal) for the one group of user's who shares same frequency resources (MU-MIMO) channel response, keep other users' channel and the numerical value that frequency shift (FS) is in their recent renewals.The nearest estimation of supposing channel and frequency shift (FS) then is used for every other user, comes to be each the user's estimated frequency skew among these users in this group.In primary iteration, algorithm adopts the starting point of previous estimation of calculating as old user, and new user has ideal channel response and do not have frequency error.When reaching the update times that is programmed, stop iteration.Normally, under the MU-MIMO situation, can only be a reception antenna estimated frequency error, and that estimation can be used for the antenna of other activation then.

Fig. 1 has described the exemplary communication environment 100 that the present invention can operate therein.As shown in Figure 1, exemplary communication environment 100 is the MU-MIMO OFDMA up links with general carrier allocation scheme.Further in the modification, invention can be used for the SC-FDMA system, also has other MIMO modes, for example single user (SU) MIMO, and this will be obvious to those skilled in the art.Exemplary communication environment 100 comprises that base station 110 and a plurality of subscriber equipment (UE) device 120-1 are to 120-N _UEBase station 110 has a plurality of reception antenna 130-1 to 130-N _RXNotice that the number of antenna in following mathematical description also represents with A.Normally, as shown in Figure 1, each UE 120 uses corresponding allocation of carriers (CA), frequency error ε and passes through specific channel response H, sends.Wherein, H for each transmitter receiver antenna to being different.

Fig. 2 has described exemplary general carrier allocation scheme 200.In the exemplary scheme 200 of Fig. 2, ten users (each has different filling patterns) share four Spatial Dimensions, and M1 is to M4, and ten frequency bands, and F1 is to F10.Therefore, as shown in Figure 2, a plurality of users can share identical frequency channels.For each user, frequency error ε can be different.In addition, as shown in Figure 2, if distribute a plurality of frequency bands for a given user, they can not be continuous.

Suppose

Notice that the actual value that illustrates only is the example of the Typical Disposition of LTE.The frequency band that has distributed has F, f=0...F-1.

Each frequency band has M _fIndividual user, 0≤m≤M _f-1.Can reach four every bandwidth assignment of user, M _f≤ 4.

S _{M, f}(n) be the subcarrier of user m and band f.The different frequency bands that distributed should not have overlapping.

The fast Fourier transform (FFT) size, N, wherein N typically equals 1024.

A reception antenna arranged, a=0...A-1.

Formula

The signal at reception antenna a place is provided by following:

$r^a\left(k\right)=\underset{f=0}{\overset{F-1}{\mathrm{\&Sigma;}}}\underset{m=0}{\overset{M_f-1}{\mathrm{\&Sigma;}}}{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HSA00000099574500011.png,HSA00000099574500051.png"\; state="\{\{state\}\}">e</figure-callout>}}^j\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_{m,f}\left(l\right)s_{m,f}(k-l)+w\left(k\right)$

ε wherein _{M, f}Be the frequency error of the band f that normalizes to subcarrier spacing of user m, L is all users' maximum channel length and s _{M, f}Be S _{M, f}IFFT.

At frequency domain, extract after Cyclic Prefix and the FFT, for each subcarrier n:

$R^a\left(n\right)=\underset{f=0}{\overset{F-1}{\mathrm{\&Sigma;}}}\underset{m=0}{\overset{M_f-1}{\mathrm{\&Sigma;}}}\underset{r=0}{\overset{N-1}{\mathrm{\&Sigma;}}}f(r,{\mathrm{\&epsiv;}}_{m,k})H_{m,f}\left({(n-r)}_N\right)S_{m,f}\left({(n-r)}_N\right)+W\left(n\right)$

Wherein

Be the frequency error index

FFT, (.) _NExpression mould N index.

The ICI item number of offsetting can be restricted to ± N _ICISupposing has the frequency protection band at the two ends of band, does not typically need then to carry out circular convolution and can abandon subscript N, as follows:

$R^a\left(n\right)=\underset{f=0}{\overset{F-1}{\mathrm{\&Sigma;}}}\underset{m=0}{\overset{M_f-1}{\mathrm{\&Sigma;}}}\underset{r=-N_{\mathrm{ICI}}}{\overset{N_{\mathrm{ICI}}}{\mathrm{\&Sigma;}}}{f(r,{\mathrm{\&epsiv;}}_{m,f})H}_{m,f}(n-r)S_{m,f}(n-r)+W\left(n\right)$

Fig. 3 is the flow chart of the exemplary realization of frequency shift (FS) that describe to introduce feature of the present invention and channel response estimation procedure 300.Normally, frequency shift (FS) and channel response estimation procedure 300 are estimated ε together for all users _{M, f}And H _{M, f}Typically, frequency shift (FS) and channel response estimation procedure 300 are realized by the processor of the base station among Fig. 1 110.

As shown in Figure 3, frequency shift (FS) and channel response estimation procedure 300 adopt counter j to follow the tracks of number of iterations, the frequency band that adopts counter f to follow the tracks of to have distributed and adopt counter m to come user in the tracing preset frequency band.

At each time slot, when the training piece arrives in step 310, demodulated reference signal (DMRS) for example,

1. for antenna a=0, carry out j=0...J-1 iteration of following algorithm:

A. for all frequency band fi=0..F-1 that has distributed

I. all subcarriers that are n frequency band that generates calculate:

$y^{{\left(j\right)}^a}\mathrm{fi}\left(n\right)=R^a\left(n\right)-\underset{f=0}{\overset{F-1}{\mathrm{\&Sigma;}}}\underset{m=0}{\overset{M_f-1}{\mathrm{\&Sigma;}}}\underset{r=-N_{\mathrm{ICI}}}{\overset{N_{\mathrm{ICI}}}{\mathrm{\&Sigma;}}}f(r,{\widehat{\mathrm{\&epsiv;}}}_{m,f}){\hat{H}}_{m,f}(n-r)S_{m,f}(n-r)+\underset{m=0}{\overset{M_f-1}{\mathrm{\&Sigma;}}}{\hat{H}}_{m,\mathrm{fi}}\left(n\right)S_{m,\mathrm{fi}}\left(n\right)$

Wherein

Be ε _{M, f}Nearest estimated value and

Be H _{M, f}Nearest estimated value.Also be appreciated that in first time iteration new user has in step 315

With

For the out-of-band n value of having distributed,

Ii. use

In step 320, estimate the channel response of this band for all MU-MIMO users In step 330, upgrade channel response then for all MU-MIMO users

Iii. for mi=0...M _f-1, be all subcarriers of n this frequency band that generates and the N in each phase adjacent band _ICIIndividual subcarrier calculates:

Wherein Be ε _{M, f}Nearest estimated value and

Be H _{M, f}Nearest estimated value.In step 340, search makes following formula maximized

Value.

$c\left({\widehat{\mathrm{\&epsiv;}}}_{\mathrm{mi},\mathrm{fi}}\right)=\underset{n}{\mathrm{\&Sigma;}}\mathrm{Re}\{x^{{\left(j\right)}^a}\mathrm{fi},\mathrm{mi}\left(n\right)\underset{r=-N_{\mathrm{ICI}}}{\overset{N_{\mathrm{ICI}}}{\mathrm{\&Sigma;}}}f(r,{\widehat{\mathrm{\&epsiv;}}}_{\mathrm{mi},\mathrm{fi}}){\hat{H}}_{\mathrm{mi},\mathrm{fi}}(n-r)S_{\mathrm{mi},\mathrm{fi}}(n-r)\}$

Be all user's renewal frequency skews then in step 350.For antenna a=1..A-1, use from the frequency error of antenna a=0 and estimate and estimate channel response.

Fig. 4 has described f (r, ε _{M, f}), the FFT of frequency error index, and Fig. 5 described the signal to noise ratio (snr) restriction of being forced by this influence, is f (r, ε _{M, f}) middle function of offsetting the number of item.As shown in Figures 4 and 5, typically, enough offset the contribution of little quantity.For example, because SNR is limited in around the 23.6dB, can satisfy the demand so offset 11 in every side of each carrier wave.This means the interference that only needs to offset from the subcarrier of other subcarrier of same block and adjacent block.

Conclusion

Though described exemplary embodiment of the present invention around digital logic block, but as being obvious for those skilled in the art, can be by in numeric field, in the hardware of circuit unit or state machine or in the combination of software and hardware, realizing various functions as the treatment step in the software program.Such software can be used for, for example, and digital signal processor, microcontroller or all-purpose computer.Such hardware and software can be included in the circuit of being realized by integrated circuit.

Therefore, function of the present invention can be realized by method and the form of putting into practice the device of those methods.One or more aspect of the present invention can realize by the form of program code, for example, whether be stored in the storage medium, be loaded into and/or carry out or on some transmission mediums, transmit by machine, wherein, when program code is loaded into when carrying out in the machine (as computer) and by machine, this machine becomes puts into practice device of the present invention.When on general processor, realizing,, the program code segments associative processor carries out the apparatus operating that is similar to particular logic circuit thereby providing.

Be to be understood that the embodiment and the modification that illustrate with describe only are the descriptions of principle of the present invention here, and those skilled in the art can realize various changes, and not depart from the scope of the present invention and spirit.

Claims (10)

1. alternative manner that is used to skew of a plurality of frequency resource estimated frequencies and channel response may further comprise the steps:

For the one group of user who shares given in a described frequency resource frequency resource estimates channel response; And

Be the described user's estimated frequency skew in described group, wherein the channel response of the user in described group and frequency shift (FS) do not remain on the numerical value of its recent renewal.

2. the method for claim 1, wherein user's channel response is initially ideal channel response.

3. the method for claim 1, wherein user's frequency shift (FS) is approximately zero at first.

4. the method for claim 1, wherein said frequency resource is provided by the MU-MIMO communication system.

5. the method for claim 1 is wherein when satisfying predetermined threshold and described iteration stopping during when the iteration that reaches predetermined number one or more in the two.

6. the method for claim 1 wherein is that first antenna determines that described frequency shift (FS) and the described frequency shift (FS) that is determined are used at least one extra antenna.

7. the method for claim 1 is wherein carried out the step that described estimation channel response and estimated frequency are offset basically simultaneously.

8. the method for claim 1, wherein said method adopts space-alternating broad sense expectation maximization SAGE algorithm in frequency domain.

9. system that is used to skew of a plurality of frequency resource estimated frequencies and channel response comprises:

Memory; And

At least one processor is coupled to described memory, is applicable to:

For the one group of user who shares given in a described frequency resource frequency resource estimates channel response; And

Be the described user's estimated frequency skew in described group, wherein the channel response of the user in described group and frequency shift (FS) do not remain on the numerical value of its recent renewal.

10. system as claimed in claim 9 wherein carries out the described estimation of described channel response and described frequency shift (FS) basically simultaneously.

Images